Holders now used in the field of automated clinical analysis may employ mechanical grip devices for gripping sample containers after the holders are positioned over the upper portions of the containers. In addition to often being complex and hard to clean, some mechanical grippers have other disadvantages. These grippers may not readily accommodate sample containers having different diameters or varying cap configurations. Furthermore, in the event of a power or other failure, a mechanical gripper may lose its grip on the container. The containers may be dropped, thereby spilling their contents.
A further disadvantage may be present when a holder with a mechanical grip device is employed in a mixer or shaker device which inverts the holder and the containers in order to mix the contents of the containers. Since a mechanical gripper often grips the upper portion of the sample containers but not their caps, a cap may separate from a container during the inverting process thereby spilling the container contents.